1. Field of the Invention
The present invention relates to an exposure method and apparatus, a method of making an exposure apparatus, a device, and a device manufacturing method. More particularly, the present invention relates to an exposure method and apparatus which are used when a circuit device such as a semiconductor device or liquid crystal display device is manufactured in a lithography process, a method of making an exposure apparatus, and a device and the method of manufacturing the device using the exposure method and apparatus.
2. Description of the Related Art
Currently, at the sites which manufacture semiconductor devices, circuit devices with minimum line width of about 0.3 to 0.35 xcexcm (64M (Mega) bit D-RAMs and the like) are mass-produced by using reduction projection exposure apparatus, so-called steppers, using the i line from mercury lamps that has a wavelength of 365 nm as an illumination light. At the same time, the introduction of exposure apparatus, which are designed to mass-produce circuit devices of the next generation that have an integration degree equivalent to those in the class of 256 Mbit and 1G (Giga) bit D-RAMs and minimum line widths of 0.25 xcexcm, has begun.
As the exposure apparatus for manufacturing circuit devices of the next generation, a scanning exposure apparatus based on the step-and-scan method is being developed. This apparatus uses an ultraviolet pulse laser beam with a wavelength of 248 nm from a KrF excimer laser source or an ultraviolet pulse laser beam with a wavelength of 193 nm from an ArF excimer laser source as an illumination light. A scanning exposure apparatus then linearly scans a mask or a reticle (to be generically referred to as a xe2x80x9creticlexe2x80x9d hereinafter) on which a circuit pattern is drawn and a wafer serving as a photosensitive substrate, relatively to the projection field of a reduction projection optical system. This allows the transfer of the entire pattern within a shot area on the wafer by repeating the inter-shot stepping operation and the scanning exposure operation.
There is no doubt that the integration degree of semiconductor devices will further increase and will shift from 1 Gbit to 4 Gbit in the future. In this case, the device rule will become about 0.1 xcexcm, i.e., 100 nm L/S, which gives rise to various technical issues when an exposure apparatus uses an ultraviolet pulse laser beam having a wavelength of 193 nm. The resolution of an exposure apparatus which, in turn, indicates a device rule (a practical minimum line width), is generally expressed using the following formula (1), using an exposure wavelength xcex and the numerical aperture N.A. of a projection optical system:
(resolution)=kxcex/N.A.xe2x80x83xe2x80x83(1)
where k, in this case, is called a k factor and is a positive constant equal to or less than 1, which varies depending on the characteristics of the resist used.
As is obvious from equation (1), in order to increase the resolution, it is extremely effective to decrease the wavelength xcex. For this reason, recently, an EUV exposure apparatus using light in the soft X-ray region of 5 to 15 nm in wavelength (in this specification, this light will also be referred to as xe2x80x9cEUV (Extreme Ultraviolet) lightxe2x80x9d) as the exposure light has been developed. Such an EUV exposure apparatus has recently attracted a great deal of attention as a promising candidate for an exposure apparatus of the generation after the next, having a minimum line width of 100 nm.
In the EUV exposure apparatus, a reflection type reticle is generally used. This reflection type reticle is obliquely irradiated with illumination light, and light reflected by the reticle surface is projected on a wafer through a projection optical system. As a consequence, a pattern, which is irradiated with the illumination light in an illumination area on the reticle, is transferred onto the wafer. This EUV exposure apparatus employs a scanning exposure method, in which a ring-shaped illumination area is set on the reticle, and the reticle and wafer are scanned relative to the projection optical system, thereby sequentially transferring the entire pattern on the reticle onto the wafer through the projection optical system.
At the wavelength (5 to 15 nm) of light used in the EUV exposure apparatus, no material can efficiently transmit light without any absorption. Inevitably, a reflection type reticle must be used. In addition, since it is difficult to form a beam splitter, the reticle must be obliquely irradiated with illumination light.
For this reason, the projection optical system becomes non-telecentric on the reticle side. As a consequence, the displacement of the reticle along the optical axis appears on the wafer as a magnification change in the longitudinal direction of a ring-shaped exposure area (an area on the wafer which corresponds to the above ring-shaped illumination area on the reticle), and as a positional change in the transversal direction.
This technique will be described in more detail with numerical values. Assuming that a projection optical system having a resolution of 100 nm L/S is designed by using EUV light having a wavelength of 13 nm as exposure light, then Equation (1) can be rearranged into the following equation (2).
N.A.=kxcex/(resolution)xe2x80x83xe2x80x83(2)
If, for example, k=0.8, then the necessary N.A. to obtain a resolution of 100 nm L/S is N.A.=0.104 is approximately equal to 0.1. The N.A. is a value at the wafer side, and apparently, differs from that at the reticle side.
Assuming that the projection magnification of the projection optical system is xc2xc, which is generally used in a conventional deep ultraviolet exposure apparatus (DUV exposure apparatus) with the i line, g line, KrF excimer laser, or ArF excimer laser as exposure light, when the N.A. at the wafer side is 0.1, then the N.A. at the reticle side is 0.025, being xc2xc that of the wafer side. This means, that illumination light applied to the reticle has a divergence angle of about xc2x125 mrad with respect to a principal ray. In order to prevent incident light and reflected light from overlapping, the minimum incident angle must be at least 25 mrad or more.
For example, referring to FIG. 17, if an incident angle xcex8 (=outgoing angle xcex8) is 50 mrad, a transverse shift xcex5 of a circuit pattern drawn on a reticle R with respect to a Z-direction displacement xcex94Z of the pattern surface of the reticle R (also referred to as xe2x80x9cthe Z-direction displacement of a reticlexe2x80x9d as needed) can be given as:
xcex5=xcex94Z tanxcex8xe2x80x83xe2x80x83(3)
As is obvious from the equation (3), when, for example, the reticle R is displaced by 1 xcexcm in the vertical direction (Z direction) as in FIG. 17, the transverse shift of an image on the reticle pattern surface becomes about 50 nm, and the image shift of 12.5 nm being xc2xc the transverse shift, occurs on the wafer. The allowable overlay error in the semiconductor process of a device rule of 100 nm L/S is said to be 30 nm or less, thus an overlay error as large as 12.5 nm caused by a displacement of a reticle in the Z direction alone poses a serious problem. This is because overlay errors of about 10 nm can be caused by other factors, e.g., alignment accuracy of a reticle and wafer, wafer stage alignment accuracy including stepping accuracy, or the distortion of the projection optical system.
As described previously, when EUV light having a wavelength of 5 to 15 nm is used in the EUV exposure apparatus, no material can efficiently transmit in this bandwidth without any absorption. Inevitably, an all-reflection optical system formed by only several mirrors (reflection optical elements) must be used as a projection optical system, which makes it difficult to control projection magnification and causes a serious problem.
Projection magnification is generally controlled in conventional deep ultraviolet exposure apparatus (DUV exposure apparatus) which uses KrF excimer lasers and the like as a light source by (1) changing the distances between lenses and (2) changing the pressures in closed chambers between lenses. In practice, however, it is not easy to control the projection magnification by changing the distances between the mirrors, or changing the curvatures of the mirrors as in the distances between lenses. In addition, since EUV light is absorbed by gases, the entire optical path must be under vacuum, therefore prohibiting the method of changing the air pressures in the projection optical system.
One promising method of controlling the projection magnification in an EUV exposure apparatus is utilizing the phenomenon described earlier where the reticle displacement along the optical axis appears as a magnification change in the longitudinal direction of an exposure area on a ring on a wafer. That is, a method of controlling the projection magnification by intentionally displacing the reticle in the optical axis direction of the projection optical system is promising.
For example, as in the case shown in FIG. 17, when the tilt of a light beam on the reticle side is 50 mrad, if the radius of a ring field (ring-shape illumination area) is, for example, 200 nm on the reticle side, and the reticle R moves away from the projection optical system by 1 xcexcm, the radius of the ring field becomes (200 nm+50 nm). That is, the reticle image (pattern image) projected onto the wafer is enlarged by (50xc3x9710xe2x88x929)÷(200xc3x9710xe2x88x923)=0.25xc3x9710xe2x88x926=0.25 ppm, whereas the reticle image is reduced when the reticle R approaches the projection optical system.
A wafer is known to increase or decrease in size by 10 ppm or more relative to the original wafer size after processing. In the case above, in order to control magnification by 10 ppm, the reticle R must be vertically translated in the Z direction by 10÷0.25xc3x971=40 xcexcm. The problem, is, however, when the projection magnification is controlled 10 ppm by vertically moving the reticle by 40 xcexcm, the displacement of the reticle appears as a transverse shift (image shift). Not only does the reticle image which is projected onto the ring-shape exposure area on the wafer expand by 10 ppm in the longitudinal direction, but also appears as a position change of 40xc3x9712.5=500 nm in the widthwise direction (scanning direction). In lithography where a line width of 100 nm is required, about ⅓ the line width, i.e., 30 nm, can be acceptable as a total overlay, therefore, an image shift of 50 nm due to magnification cannot be allowed.
Under the circumstances, with an exposure apparatus employing an optical system that is non-telecentric on the reticle side, e.g., an EUV exposure apparatus, a new technique to reliably reduce an overlay error accompanying a change in projection magnification urgently needs to be developed.
The present invention has been made in consideration of the situation above, and has as its first object to provide an exposure apparatus that can prevent or sufficiently suppress a deterioration in overlay accuracy caused by adjusting (or changing) the optical characteristics including the imaging characteristics (e.g., magnification) of a projection optical system.
It is the second object of the present invention to provide an exposure method which can prevent or sufficiently suppress a deterioration in overlay accuracy caused by adjusting (or changing) the optical characteristics including the imaging characteristics (e.g., magnification) of a projection optical system.
According to the first aspect of the present invention, there is provided a first exposure apparatus which transfers a pattern of a mask onto a substrate, comprising; an illumination system, which has a light source, and which irradiates the mask with an illumination light for exposure, a projection optical system, which is arranged between the mask and the substrate, and which projects the illumination light outgoing from the mask onto the substrate, a magnification changing unit, which changes a projection magnification of the projection optical system, a substrate stage which holds the substrate, a mark detection system, which has a photoelectric device, and which detects a mark located on the substrate stage, and a correction unit which is electrically connected to the magnification changing unit and the mark detection system, and which corrects a shift of a projection position of a pattern on the mask after a magnification change by using a baseline of the mark detection system on transferring the pattern of the mask onto the substrate, the baseline being obtained in consideration of the shift at the magnification change which is made by the magnification changing unit.
In this case, xe2x80x9ca mark located on the substrate stagexe2x80x9d includes an object mounted on the substrate stage, e.g., a mark located on the substrate, as well as a mark such as a reference mark located on the substrate stage itself. In this specification, the term xe2x80x9ca mark located on the substrate stagexe2x80x9d is used.
In addition, xe2x80x9cthe baseline amountxe2x80x9d of the mark detection system has a meaning similar to the general meaning of this term. More specifically, the baseline amount is information about the positional relationship between the detection center of the mark detection system and the projection position of the mask pattern on the substrate stage, and is used for, for example, position control on the substrate stage (substrate). In this specification, the term xe2x80x9cbaseline amountxe2x80x9d is used in this sense.
In the first exposure apparatus according to the present invention, when the mask is irradiated with illumination light for exposure from the illumination system, the illumination light outgoing from the mask is projected onto the substrate by the projection optical system. As a consequence, a pattern in an area on the mask illuminated with the illumination light for exposure is transferred onto the substrate. When the projection magnification of the projection optical system is changed by the magnification changing unit on transferring this mask pattern, the correction unit corrects the shift of the projection position of the mask pattern by using the baseline amount of the mark detection system which corresponds to the magnification after the change. This makes it possible to prevent or sufficiently suppress deterioration in overlay accuracy due to a change in the projection magnification.
In the first exposure apparatus according to the present invention, at least one reference mark including a specific reference mark can be provided on the substrate stage, and the exposure apparatus can further comprise a position detection system, which has a photoelectric device and which detects a positional relationship between the specific reference mark and a projection position of a pattern image of the mask on the substrate stage, and the correction unit can include a control unit, which is electrically connected to the mark detection system and the position detection system, and which calculates the baseline amount which corresponds to the magnification change, based on a result obtained by detecting the positional relationship by using the position detection system, and a result can be obtained by detecting one of the specific reference mark on the substrate stage and a different reference mark which relationship with the specific reference mark is predetermined by using the mark detection system. In this case, when the projection magnification of the magnification changing unit is changed on transferring a mask pattern, the control unit which structures a correction unit obtains the baseline amount of the mark detection system which corresponds to the magnification after the change. To obtain the amount, the controller uses the position detection system to detect a positional relationship between the specific reference mark on the substrate stage and a projection position of a pattern image of the mask on the substrate stage, and the mark detection system to detect the specific reference mark or a different reference mark (the relationship with the specific reference mark is predetermined). That is, the positional relationship between the projection position of a mask pattern image on the substrate stage and the detection center of the mark detection system is obtained. In short, after the change in magnification, the correction unit actually measures the baseline amount, and corrects the positional shift of the projection position of the pattern image of the mask on the substrate due to the change in projection magnification by using the measurement result. This therefore makes it possible to prevent or sufficiently suppress a deterioration in overlay accuracy due to a change in projection magnification.
When a baseline amount is to be actually measured after the projection magnification is changed as described above, it is preferable that the mark detection system includes a focus detection system, and the exposure apparatus further comprises an adjustment unit which adjusts a position of the substrate stage in an optical axis direction to position the mark to a focal position of the mark detection system, based on a detection result obtained by the focus detection system upon detecting a mark located on the substrate stage by using the mark detection system. In this case, in measuring a baseline amount, when the mark detection system is to be used to detect a specific reference mark on the substrate stage or a reference mark (whose relationship with the specific reference mark is predetermined) different from the specific reference mark, the reference mark can be detected by adjusting the position of the substrate stage. This adjustment is performed based on the detection result obtained by the focus detection system, in which the reference mark as a detection object is positioned at the focal position of the mark detection system. Accordingly, when alignment measurement of the substrate is performed before exposure, high-precision position control on the substrate can be performed by translating the substrate to the focal position of the mark detection system in the manner above and detecting an alignment mark on the substrate using the mark detection system.
In the first exposure apparatus according to the present invention, at least one reference mark including a specific reference mark can be provided on the substrate stage, the exposure apparatus further comprising a position detection system, which has a photoelectric device, and which detects a positional relationship between the specific reference mark and a projection position of a pattern image of the mask on the substrate stage, and the correction unit can include a memory unit which stores a baseline amount of the mark detection system, the baseline amount calculated by a detection result of the position detection system, and by a result obtained by detecting one of the specific reference mark on the substrate stage and a different reference mark whose relationship with the specific reference mark is predetermined by using the mark detection system, and a calculation unit, which is electrically connected to the memory unit and the magnification changing unit, and which corrects the baseline amount stored in the memory unit in accordance with the magnification change by calculation. In this case, the baseline amount is calculated in accordance with the detection result obtained by the position detection system and the result obtained by detecting one of a specific reference mark on the substrate stage and a different reference mark whose relationship with the specific reference mark is predetermined by using the mark detection system and is stored in the storage unit in advance. When the projection magnification of the projection optical system is changed by the magnification changing unit when transferring a mask pattern, the calculation unit structuring the correction unit corrects the baseline amount stored in the storage unit by a calculation that uses the magnification changed by the magnification changing unit. This baseline amount of correction is performed based on, for example, the relationship between a control value of the magnification changing unit and the positional shift amount of the mask pattern image on the substrate. As described above, according to the present invention, only by performing an actual baseline measurement and storing the result in the memory unit in advance, can the positional shift of the projection position of a pattern image of a mask on the substrate due to a change in projection magnification be corrected by calculation alone upon a magnification changing operation. This makes it possible to prevent or sufficiently suppress deterioration in overlay accuracy due to a change in projection magnification. In addition, throughput can be increased.
In the first exposure apparatus according to the present invention, when the projection magnification is changed by the magnification changing unit and the baseline amount of the mark detection system is to be actually measured, or when a baseline amount corresponding to the projection magnification after the change is to be obtained by correcting the baseline amount obtained in advance by calculation, if the illumination light for exposure is light in the soft X-ray region, it is preferable that the position detection system is a aerial image sensor which is provided on the substrate stage, and includes a fluorescent material, a thin film made on a surface of the fluorescent material, the thin film structured of one of a reflecting layer and an absorbing layer of the illumination light for exposure, the thin film having an opening formed which also serves as the specific reference mark, and a photoelectric conversion device which photoelectrically converts light generated from the fluorescent material, where the illumination light for exposure reaches the fluorescent material via the opening on conversion. In this case, as described above, regardless of the fact that there is no material that transmits light in the soft X-ray region in general, the position detection system, i.e., the aerial image sensor, can perform a spatial image measurement by using such light as exposure illumination light. Therefore, the positional relationship between the specific reference mark (the above opening) on the substrate stage and the projection position of the pattern image of the mask on the substrate stage can be easily detected by using this position detection system.
In the first exposure apparatus according to the present invention, various projection magnification changing methods can be used. For example, the magnification changing unit can be formed from a unit which drives the mask in an optical axis direction of the projection optical system. Not only in the case of a projection optical system that is non-telecentric on the object surface side (mask side), but also in the case of a projection optical system that is telecentric on both sides, it is practically difficult to manufacture an optical system that is perfectly telecentric (at each image height within the projection field). In either case, when a mask is driven in the optical axis direction of the projection optical system, the projection magnification (or distortion) of the projection optical system changes regardless of whether the projection optical system is a refraction optical system, reflection/refraction optical system, or reflection optical system. Therefore, the projection magnification can be easily changed by using this feature.
In the first exposure apparatus according to the present invention, if the projection optical system is an optical system which includes a reflection optical element, the magnification changing unit can be an optical characteristic changing unit which changes optical characteristics of the projection optical system. In this case, the optical characteristic changing unit may be a unit for changing the distances between a plurality of reflection optical elements, or may be a unit that changes a curvature of the reflection optical element.
In the first exposure apparatus according to the present invention, the projection optical system can be an optical system which includes a reflection optical element, and the exposure apparatus can further comprise a mask stage which holds the mask, and a driving unit, which is connected to the mask stage and which synchronously moves the mask stage and the substrate stage in a first direction perpendicular to an optical axis direction of the projection optical system, and the magnification changing unit is a unit which changes the magnification of the projection optical system in a second direction perpendicular to the optical axis direction and the first direction by driving the mask in the optical axis direction of the projection optical system via the mask stage.
In such a case, when a mask is irradiated with illumination light for exposure from the illumination system, the illumination light outgoing from the mask is projected onto a substrate by the projection optical system, and a pattern in an area on the mask which is irradiated with the illumination light is transferred onto the substrate. On transferring the mask pattern, the driving unit synchronously moves the mask stage and substrate stage in the first direction perpendicular to the optical axis direction of the projection optical system. With this operation, the entire mask pattern is transferred onto the substrate by scanning exposure. In addition, the magnification changing unit is a unit for changing the magnification in the second direction which is perpendicular to the optical axis direction of the projection optical system and the first direction. This is performed by driving the mask stage in the optical axis direction of the projection optical system. Thus, the projection magnification in the second direction can be easily controlled and the magnification adjustment in the first direction (scanning direction) can be easily implemented by controlling the synchronous speed ratio. Furthermore, the correction unit can correct the positional shift of the projection position of a pattern image of the mask on the substrate due to a change in projection magnification. Accordingly, this makes it possible to prevent or sufficiently suppress deterioration in overlay accuracy due to a change in projection magnification, as well as simplify magnification control. In this case, the illumination light for exposure is not specifically limited. For example, the illumination light can be light in the vacuum ultraviolet range. Or the projection optical system may be a reflection optical system configured by only reflection optical elements, and the mask can be a reflection type mask.
As described above, if a combination of a reflection optical system constituted by reflection optical elements alone and a reflection type mask is used, the illumination light for exposure can be light in the soft X-ray region.
The first exposure apparatus according to the present invention can further comprise: a focal position detection system which detects a position of the substrate on the substrate stage in an optical axis direction of the projection optical system; and a stage control unit, which is electrically connected to the focal position detection system, and which offsets the focal position detection system which corresponds to a driving amount of the mask in the optical axis direction by the magnification changing unit, and feedback-controls the position of the substrate stage in the optical axis direction based on a detection result obtained by the focal position detection system. In this case, the position of the substrate in the optical axis direction can be set to the focal position of the projection optical system on transferring the mask pattern by the stage control unit. In addition, in particular, when at least one reference mark including a specific reference mark is provided on the substrate stage and the apparatus further comprises a position detection system which detects the positional relationship between the specific reference mark and the projection position of the pattern image of the mask on the substrate stage, the specific reference mark can be set to the focal position of the projection optical system in detecting the positional relationship between the specific reference mark and the projection position of the pattern image of the mask on the substrate stage using the position detection unit to detect a baseline amount. This makes it possible to perform high-precision detection without any focus error, and as a consequence, the baseline amount can be obtained more accurately.
In the first exposure apparatus according to the present invention, the magnification may be changed by the magnification changing unit in accordance with a given target magnification for the purpose of correcting thermal deformation of a mask or the like. However, if the apparatus further comprises a detection unit which detects a plurality of alignment marks on the substrate by using the mark detection system prior to transfer of the pattern of the mask onto the substrate, the magnification changing unit can change the magnification based on position detection results of the plurality of alignment marks of the detection unit. In this case, the actual magnification change on the substrate is obtained based on the detection results on the alignment marks, and the projection magnification is changed by the magnification changing unit in accordance with the magnification change. This improves the overlay accuracy.
In the first exposure apparatus according to the present invention, the projection optical system may be non-telecentric on the mask side.
According to the second aspect of the present invention, there is provided a second exposure apparatus which repeatedly transfers a pattern of a mask onto a substrate, comprising: an illumination system, which has a light source and which irradiates the mask with an illumination light for exposure; a projection optical system which is arranged between the mask and the substrate and projects the illumination light for exposure outgoing from the mask onto the substrate; a substrate stage which holds the substrate; a mark detection system which has a photoelectric device and detects a mark located on the substrate stage; a judgement unit which judges whether it is necessary to update a baseline amount of the mark detection system based on a predetermined judgement condition; a baseline updating unit which is electrically connected to the judgement unit and calculates a new baseline amount when a result of the judgement unit is affirmative; and a stage control unit which is electrically connected to the judgement unit and the baseline updating unit and controls a position of the substrate stage by using the baseline amount of the mark detection system which is obtained prior to transfer of the pattern of the mask onto the substrate when the result of the judgement unit is negative, and by using the new baseline amount to transfer the pattern of the mask onto the substrate when the result of the judgement unit is affirmative.
According to this aspect, while mask patterns are repeatedly transferred onto a substrate, the judgement unit determines, based on a predetermined condition, whether it is necessary to update the baseline amount of the mark detection system, and the baseline updating unit calculates a new baseline amount when a result of the judgement unit is affirmative. And with the stage control unit, if the judgement result obtained by the judgement unit is negative, the stage control unit controls the position of the substrate stage by using the baseline amount of the mark detection unit which is obtained upon transferring the mask patterns onto the substrate. If the judgement result obtained by the judgement unit is affirmative, the stage control unit uses the updated baseline amount obtained upon transferring the mask patterns onto the substrate to control the substrate stage position. As the predetermined condition above, if a condition that allows estimation of the possibility that the baseline amount will vary beyond the allowable value is set, in the case that the baseline amount varies within the allowable value and the positional shift of the transferred image of the mask pattern can be neglected, then the position of the substrate stage during exposure is controlled by using the baseline amount obtained in advance. If the baseline amount is likely to vary beyond the allowable value and the positional shift of the transferred image of the mask pattern cannot be neglected, then a new baseline amount is obtained by measurement (or calculation) and the position of the substrate stage during exposure is controlled by using the newly obtained baseline amount. This makes it possible to prevent or sufficiently suppress the positional shift of the projection position of the mask pattern image on the substrate. In addition, since the baseline amount is re-measured (or re-calculated) only when required, throughput can be increased.
In this case, various conditions are conceivable as the above determination condition. For example, the judgement unit can determine whether it is necessary to update the baseline amount of the mark detection system, depending on whether the substrate, as a object onto which the mask pattern is to be transferred, is a first substrate of a lot.
According to the third aspect of the present invention, there is provided a first exposure method which transfers a pattern formed on a mask onto a substrate through a projection optical system while synchronously moving the mask and the substrate, wherein on transferring the pattern of the mask irradiated with the illumination light onto the substrate through the projection optical system, a pattern surface of the mask is irradiated with an illumination light for exposure at a predetermined incident angle, a desired projection magnification of the projection optical system in a direction perpendicular to the synchronously moving direction is set, a position of the substrate is controlled by using a baseline amount of a mark detection system which is obtained in consideration of a shift of a projection occurring when the desired projection magnification is set, and the baseline amount is used to detect an alignment mark on the substrate.
According to this aspect, in irradiating the pattern surface of a mask with exposure illumination light at a predetermined incident angle (including an incident angle of 0xc2x0) and transferring a pattern of the mask irradiated with the exposure illumination light onto a substrate through the projection optical system, when the projection magnification of the projection optical system is set to a desired value in a direction perpendicular to the synchronous moving direction, the position of the substrate is controlled by using the baseline amount of the mark detection system for detecting alignment marks on the substrate which corresponds to the baseline amount after this setting. In this case, the projection magnification in the synchronous moving direction, can be controlled by adjusting the synchronous velocity ratio between the mask and the substrate. This makes it possible to change the projection magnification and prevent deterioration in overlay accuracy due to the change.
In this case, the baseline amount corresponding to the desired projection magnification can be a baseline amount detected after the desired projection magnification is set. Alternatively, the baseline amount corresponding to the desired projection magnification can be a baseline amount previously obtained and corrected by calculation in accordance with the projection magnification. In the latter case, projection magnification can be changed, as well as prevent deterioration in overlay accuracy due to the change, without performing any baseline measurement upon exposure.
In the first exposure method according to the present invention, the mask may be a reflection type mask, and the projection optical system may be a reflection optical system.
According to the fourth aspect of the present invention, there is provided a second exposure method which transfers a pattern formed on a reflection type mask onto a substrate through a projection optical system which is configured only of a plurality of reflection optical elements while synchronously moving the reflection type mask and the substrate, wherein optical characteristics of the projection optical system are adjusted prior to transfer, and a positional relationship between a projection area of a pattern image and the substrate during the synchronous movement is adjusted so as to compensate a shift of the projection area in an image field of the projection optical system.
According to this aspect, the optical characteristics of the projection optical system are adjusted before the pattern of the reflection type mask is transferred onto the substrate through the projection optical system which includes only a plurality of reflection optical elements. This adjustment is performed by synchronously moving the reflection type mask and the substrate. On transferring the mask pattern onto the substrate, the positional relationship between the projection area of the pattern image and the substrate during synchronous movement of the reflection type mask and substrate is adjusted. This adjustment is made so as to compensate for the shift of the projection area of the pattern image within the image field of the projection optical system, which is caused by the adjustment of the optical characteristics. This therefore makes it possible to prevent or sufficiently suppress deterioration in overlay accuracy due to the adjustment of optical characteristics.
In this case, an exposure position can be determined by positional information obtained by detecting a mark on the substrate by using a mark detecting system. The positional relationship between the projection area and the substrate can be adjusted by synchronous movement of the substrate with respect to the reflection type mask, the substrate controlled in accordance with a baseline amount of the mark detection system after adjustment of the optical characteristics and the predetermined exposure position information.
In the second exposure method according to the present invention, the synchronous movement may be performed by using one of the baseline amount of the mark detection system which is measured after adjustment of the optical characteristics and the baseline amount of the mark detection system which is calculated from the adjusted optical characteristics. More specifically, if the optical characteristics greatly change after the adjustment of optical characteristics, since the baseline amount is likely to greatly change due to the adjustment of optical characteristics, the baseline amount of the mark detection system can be actually measured. In contrast, if the optical characteristics hardly change after the adjustment of optical characteristics, the baseline amount of the mark detection system, which is calculated from the adjusted optical characteristics, can be used. In the latter case, the overlay accuracy hardly deteriorates upon usage of the calculated value obtained by correcting the baseline amount before the adjustment with the change in baseline amount, which is calculated based on the relationship between the adjustment amount of optical characteristics and the baseline amount.
In the second exposure method according to the present invention, a projection magnification of the pattern image in a direction perpendicular to the synchronous moving direction of the substrate can be adjusted by moving the reflection type mask in a direction along an optical axis of the projection optical system based on at least one of a plurality of positional information obtained by detecting a plurality of marks on the substrate by using the mark detection system and a plurality of positional information obtained by detecting a plurality of marks on the reflection type mask through the projection optical system. In this case, the expansion/contraction amount of the substrate can be obtained based on a plurality of positional information, which are obtained by detecting a plurality of marks on the substrate using the mark detection system. In addition, the magnification (or magnification change) of the mask pattern image projected on the substrate can be obtained on the basis of a plurality of positional information which are obtained by detecting a plurality of marks on the reflection type mask through the projection optical system. Therefore, the projection magnification of the pattern image in the direction perpendicular to the synchronous moving direction of the substrate can be properly adjusted by moving the reflection type mask in the optical axis direction of the projection optical system. The adjustment can be made based on either the plurality of positional information which are obtained by detecting the plurality of marks on the substrate using the mark detection system or the plurality of positional information which are obtained by detecting the plurality of marks on the reflection type mask through the projection optical system.
In the second exposure method according to the present invention, the reflection type mask is irradiated with an illumination light for exposure which principal ray tilts with respect to a pattern surface of the mask, the illumination light can be either light in a soft X-ray region or a vacuum ultraviolet light, and the projection optical system can be non-telecentric on the mask side.
According to the fifth aspect of the present invention, there is provided a third exposure method which repeatedly transfers a pattern of a mask onto a substrate through a projection optical system, comprising: a first step of monitoring a change in physical quantity which becomes a factor that changes a baseline amount of a mark detection system for detecting a mark on the substrate; a second step of judging whether it is necessary to update the baseline amount of the mark detection system, which depends on whether the physical quantity exceeds a predetermined acceptable value; and a third step of obtaining a new baseline amount when a judgement result is affirmative and controlling a position of the substrate by using the new baseline amount, controlling the position of the substrate by using the baseline amount of the mark detection system when the judgement result is negative, performing exposure.
According to this aspect, in the first step, a change in a physical quantity is monitored. This physical quantity becomes a factor that changes the baseline amount of the mark detection system for detecting marks on the substrate. In the second step, depending on whether the physical quantity has exceeded the predetermined allowable value, it is judged whether it is necessary to update the baseline amount of the mark detection system. In the third step, if the judgement result is affirmative, a new baseline amount is obtained. The new baseline amount is used to control the position of the substrate. If the judgement result is negative, the previously obtained baseline amount of the mark detection system is used to control the position of the substrate, and exposure is performed. Accordingly, in the case that the physical quantity becomes a factor which changes the baseline amount of the mark detection system, and the variation in baseline amount is likely to exceed the acceptable value, hence the positional shift of the transferred image of the mask pattern cannot be neglected, a new baseline amount is obtained by measurement (or calculation) and the position of the substrate stage during exposure is controlled by using the new baseline amount. In contrast to this, when the physical quantity falls within the predetermined acceptable value and a variation in baseline amount falls within the acceptable value, the positional shift of the transferred image of the mask pattern can be neglected. Therefore, the position of the substrate stage during exposure can be controlled by using the previously obtained baseline amount. This makes it possible to prevent or sufficiently suppress the positional shift of the projection position of the mask pattern image on the substrate. In addition, the throughput can be increased since a baseline amount is re-measured (re-calculated) only when necessary.
In the third exposure method according to the present invention, various physical quantities are conceived as the physical quantity to be monitored in the first step. For example, the monitored physical quantity can be a change in the mask due to thermal expansion. In this case, the change in the mask due to thermal expansion can be estimated based on a measurement result of a temperature distribution of the mask.
In the third exposure method according to the present invention, the physical quantity monitored in the first step is an image forming characteristic of the projection optical system.
In the third exposure method according to the present invention, if the projection optical system is an optic system including a mirror, the physical quantity monitored in the first step can be a deformation amount of the mirror.
According to the sixth aspect of the present invention, there is provided a fourth exposure method which repeatedly transfers a pattern of a mask onto a substrate through a projection optical system. The method comprises: judging whether it is necessary to update a baseline amount of a mark detection system based on a predetermined judgement condition where the mark detection system detects a mark located on a substrate stage; controlling a position of the substrate stage using the baseline amount of the mark detection system which is obtained prior to transfer of the pattern of the mask onto the substrate when a result of the judgement is negative, and using a new baseline amount to transfer the pattern of the mask onto the substrate when the result of the judgement is affirmative.
According to this aspect, while the mask pattern is repeatedly transferred onto the substrate, a judgement is made on whether to update the baseline amount of the mark detecting system in accordance with a predetermined judgement condition. And, when the judgement result is negative, the position of the substrate stage is controlled by using the baseline amount of the mark detection system, which is obtained prior to transfer of the pattern of the mask onto the substrate. When the judgement result is affirmative, the position of the substrate stage is controlled by a new baseline amount obtained upon transferring of the pattern of the mask onto the substrate. Accordingly, the predetermined judgement condition (if a condition that presumably requires a judgement as to whether the baseline amount will vary in excess of the acceptable amount is identified, as described earlier) can prevent or suppress the shift of a projection position of a mask pattern as well as increase throughput since the baseline amount is re-measured (re-calculated) only when necessary.
According to the seventh aspect of the present invention, there is provided a first method of making an exposure apparatus which transfers a pattern of a mask onto a substrate, comprising: providing an illumination system which has a light source and irradiates the mask with an illumination light for exposure; providing a projection optical system which is arranged between the mask and the substrate and projects the illumination light for exposure outgoing from the mask onto the substrate; providing a magnification changing unit which changes a projection magnification of the projection optical system; providing a substrate stage which holds the substrate; providing a mark detection system which has a photoelectric device and detects a mark located on the substrate stage; and providing a correction unit which is electrically connected to the magnification changing unit and the mark detection system and corrects a shift of a projection position of the pattern of the mask after a magnification change by using a baseline amount of the mark detection system on transferring the pattern of the mask onto the substrate, the baseline amount being obtained by consideration of the shift at the magnification change which is made by the magnification changing unit.
With this method, the exposure apparatus can be made by mechanically, optically, and electrically combining an illumination system, a projection optical system, a magnification changing unit, a substrate stage, a correction unit, and other various components and adjusting them. In this case, a static type exposure apparatus such as a step-and-repeat type exposure apparatus can be made.
The method of making an exposure apparatus according to the present invention may further comprise: the step of providing a mask stage which holds the mask; and the step of providing a driving unit which synchronously moves the mask stage and the substrate stage in a first direction perpendicular to an optical axis direction of the projection optical system. In this case, a scanning exposure apparatus based on the step-and-scan method or the like can be made, which can correct image distortion characteristics by changing/adjusting the scanning velocity of the mask stage and substrate stage and the angle in between the scanning directions.
According to the eighth aspect of the present invention, there is provided a second method of making an exposure apparatus which repeatedly transfers a pattern of a mask onto a substrate, which comprises: providing an illumination system which has a light source and irradiates the mask with an illumination light for exposure; providing a projection optical system, which is arranged between the mask and the substrate, and which projects the illumination light for exposure outgoing from the mask onto the substrate; providing a substrate stage which holds the substrate; providing a mark detection system, which has a photoelectric device, and which detects a mark located on the substrate stage; providing a judgement unit which judges whether it is necessary to update a baseline amount of the mark detection system based on a predetermined judgement condition; providing a baseline updating unit, which is electrically connected to the judgement unit, and which calculates a new baseline amount when a result of the judgement unit is affirmative; and providing a stage control unit, which is electrically connected to the judgement unit and the baseline updating unit, and which controls a position of the substrate stage using the baseline amount of the mark detection system which is obtained prior to transfer of the pattern of the mask onto the substrate when the result of the judgement unit is negative, and using the new baseline amount to transfer the pattern of the mask onto the substrate when the result of the judgement unit is affirmative.
In the lithography process, a plurality of layers of patterns can be formed on a substrate with a high overlay accuracy by performing an exposure using the exposure method according to the present invention. This makes it possible to manufacture microdevices with higher degrees of integration at a high yield. Likewise, in the lithography process, a plurality of layers of patterns can be formed on a substrate with high overlay accuracy by performing exposure using the exposure apparatus according to the present invention. This makes it possible to manufacture microdevices with higher degrees of integration at a high yield. From another point of view, the present invention is a device manufacturing method using the exposure method of the present invention and the lithography system of the present invention, and a device manufactured by the manufacturing method of the present invention.